A conventional bit holder device which holds a screw, etc. with retaining a bit body inserted in the groove on the head of the screw, etc. to facilitate a job of tightening, driving into a workpiece, or the like of the screw is disclosed in, for example, JP-A-2000-246658.
What is disclosed in that publication consists of a cylindrical body fitted on a bit body attached to an electric tool, and the cylindrical body is provided with holding means (a magnet) for holding a screw with the bit body inserted in the groove of its head.
The use of the cylindrical body has, however, makes the attachment and detachment of the bit and cylindrical bodies cumbersome, since two jobs, that is, the job of removing the bit body from the chuck of the electric tool and the job of removing the cylindrical body from the bit body are required for changing the bit body and attaching the cylindrical body to another bit body.
A bit holder device as disclosed in German Patent Publication DE10148943A1 is known as a type in which the bit body is removably held by a holder body having a shank in its rear portion. The device described in the German Patent Publication has, however, a drawback that the cylindrical body cannot be removed from the holder body.    Patent Literature 1: JP-A-2000-246658    Patent Literature 2: German Patent Publication DE10148943A1